I'm okay with steam because:

• basically everyone can sell their games on Steam (*conditions apply)
• it has a (working) offline mode
• they're putting a lot of effort into gaming on Linux
• family sharing
• it let's me integrate external games

The Blizzard launcher is just for the few games Blizzard is selling. It asked me to go online way too often. Maybe every single time, I don't remember exactly. It's a bit like that Rockstar launcher. I don't see any value in it besides auto updates.